Feeling sluggish? Bad mood? Go outside.

ROCHESTER, N.Y., June 4 (UPI) -- Those needing an energy boost and improved mood should spend some time every day outside, U.S. researchers found.

"Nature is fuel for the soul," lead author Richard Ryan, a professor of psychology at the University of Rochester in New York, said in a statement.

"Often when we feel depleted we reach for a cup of coffee, but research suggests a better way to get energized is to connect with nature."

Ryan and colleagues conducted five separate experiments involving 537 college students who were asked to experience being indoors and outdoors, view photographs, or imagine themselves in a variety of activities indoors and outdoors.

The moods and energy levels of the study participants were tracked for up to two weeks.

The findings, published in the Journal of Environmental Psychology, found across all methodologies, people said they felt more energetic after being in natural settings or imaging themselves outside.

The findings were significant for those who spent 20 minutes a day being in nature.

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